The invention relates to an anti-lock control system for the braking of wheeled vehicles wherein one pickup element to determine the speed of rotation of a wheel is associated at least with the wheels of one vehicle axle. In an evaluating circuit to which signals from the pickup elements are transmitted, control signals are alternatively produced for the pressure control units associated with the wheels to vary the brake pressure. If the signals corresponding to the wheel velocities deviate the predetermined threshold values .lambda..sub.1 or .lambda..sub.2 from the reference signals corresponding to the curve of the vehicle velocity, a control signal is normally produced when the value falls below the smaller threshold value .lambda..sub.1.
Such an anti-lock control system is known from DOS (German Unexamined Laid-Open Application) No. 2,063,944. In FIG. 2 of this reference, the small slip threshold is normally switched on. If this threshold is exceeded, then the pressure is lowered and after a predetermined time .DELTA.T, the switchover is effected to the large slip threshold. Once the large slip threshold has also been exceeded, the pressure is further lowered until the large pressure threshold has again been passed in the downward direction. In contrast thereto, if the wheel slip remains in the range defined by the two slip thresholds, then the lowering signal terminates with the switchover to the large slip threshold.
In case of slip control arrangements, the reference signal representing the vehicle speed is customarily taken from the wheel velocities, wherein the most rapidly revolving wheel determines the value of the speed reference signal. With a predetermined, small slip value, when the vehicle traverses a tight curve the rotational speed of the wheel on the inside of the curve is so much lower than the reference signal determined by the wheel on the outside of the curve that a wheel slip is simulated for the wheel on the inside of the curve corresponding to .lambda..sub.1 having been exceeded, and accordingly a brake fluid pressure lowering signal is produced. On the other hand, it is desirable to have the small slip threshold .lambda..sub.1 effective initially to insure a response of the control unit even in case of low vehicle speeds.